Glioblastoma (GBM) is a tumor of the brain and represents about 15.4% of all primary brain tumors and about 60-75% of all astrocytomas. GBM tumors increase in frequency with age, and affect more men than women. Only three percent of childhood brain tumors are glioblastomas. Standard fluorouracil-based chemotherapy can prolong survival but most patients eventually become resistant. The chemotherapy drug TMZ is standard treatment for patients with GBM. TMZ, also known as Temodar®, is an oral chemotherapy drug in the class of alkylating agent which also includes such chemotherapy agents as cisplatin, carboplatin, cyclophosphamide, melphalan and chlorambucil.
In multiple cancer types, the DNA repair protein 06-methylguanine-DNA methyl-transferase (MGMT) is a resistance marker for TMZ because it is thought that MGMT promoter methylation is associated with loss of MGMT expression and response to TMZ. The therapeutic benefit of TMZ, and other alkylating agents, depends on its ability to alkylate/methylate DNA resulting in damage to the DNA thus triggering the death of tumor cells. However, alkylating antineoplastic agents have limitations based on the fact that some tumor cells are able to repair this type of DNA damage therefore diminishing the therapeutic efficacy of TMZ. Cross-linking of double-stranded DNA by alkylating agents is inhibited by the cellular DNA-repair protein MGMT. In some tumors, epigenetic silencing of the MGMT gene prevents the synthesis of this enzyme, and as a consequence such tumors are more sensitive to killing by TMZ. Conversely, the presence of MGMT protein in tumors cells may predict poor response to TMZ and these patients receive little benefit from chemotherapy with TMZ. Thus there is a need for improved methods of treating cancers, such as gliobastoma, with TMZ by using new and improved methods of easily and accurately determining MGMT biomarker levels in patient samples.